1. Field of the Invention
The present invention relates to a clutch mechanism, which enables or disables conduction of a drive force therethrough, and a clutch system having the same.
2. Description of Related Art
An electromagnetic clutch mechanism, which enables or disables conduction of a rotational drive force from a driving-side rotator to a driven-side rotator through energization or deenergization of an electromagnet is known. In this type of the electromagnetic clutch, the electromagnet is energized to couple between the driving-side rotator and the driven-side rotator to conduct the rotational drive force from the driving-side rotator to the driven-side rotator. When the electromagnet is deenergized, the driving-side rotator and the driven-side rotator are decoupled from each other to disable the conduction of the rotational drive force from the driving-side rotator to the driven-side rotator.
However, in this type of electromagnetic clutch, at the time of coupling between the driving-side rotator and the driven-side rotator to conduct the rotational drive force, the electromagnet must be always energized throughout the period of the coupling between the driving-side rotator and the driven-side rotator (i.e., as long as the driving-side rotator and the driven-side rotator are being coupled with each other), thereby resulting in an increased electric power consumption (energy consumption) at the time of conducting the rotational drive force.
Japanese Examined Patent Publication No. H02-002007B teaches a clutch mechanism of a self-retaining type, in which a permanent magnet is used to eliminate a need for energizing the electromagnet at the time other than the time of coupling between the driving-side rotator and the driven-side rotator or the time of decoupling between the driving-side rotator and the driven-side rotator to reduce the electric power consumption.
Specifically, in the clutch mechanism of the self-retaining type, a rotor and an armature, which serve as the driving-side rotator and the driven-side rotator, respectively, are provided, and the permanent magnet is placed radially inward of the rotor. In a decoupled state of the rotor and the armature, in which the rotor and the armature are decoupled from each other, a gap (air gap) of a predetermined size (predetermined distance) is formed between the rotor and the armature by a leaf spring, which generates a repulsive force against the magnetic force (attracting force) that attracts the armature.
The air gap forms a magnetic resistance of the magnetic circuit, in which the attracting force is generated with the permanent magnet. When the gap, which has the size (distance) equal to or larger than the predetermined size (predetermined distance), is formed, the attracting force of the permanent magnet becomes smaller than the repulsive force of the leaf spring. Therefore, the rotor and the armature are maintained in the decoupled state, in which the rotor and the armature are decoupled from each other.
At the time of coupling between the rotor and the armature, the electromagnetic force is generated with the electromagnet to assist the attracting force of the permanent magnet, so that a sum of the attracting force of the permanent magnet and the attracting force of the electromagnet becomes larger than the repulsive force of the leaf spring. In this way, when the rotor and the armature are coupled with each other, the magnetic resistance is reduced. Therefore, the coupled state of the rotor and the armature is maintained even though the electromagnet is placed in the deenergized state.
At the time of decoupling between the rotor and the armature, the electromagnetic force is generated with the electromagnet to cancel the magnetic force of the permanent magnet. Thereby, the attracting force of the permanent magnet becomes smaller than the repulsive force of the leaf spring. In this way, when the rotor and the armature are decoupled from each other, the magnetic resistance is increased by the gap. Therefore, even when the electromagnet is placed in the deenergized state, the rotor and the armature are kept held in the decoupled state.
However, in the clutch mechanism of the self-retaining type recited in Japanese Examined Patent Publication No. H02-002007B, the magnetic resistance, which is generated with the air gap between the driving-side rotator (rotor) and the driven-side rotator (armature), is used to maintain the decoupled state of the driving-side rotator and the driven-side rotator. Therefore, in a case where the gap, which has the predetermined size (distance) or lager, cannot be maintained, the driving-side rotator and the driven-side rotator are coupled with each other even though the attracting force of the permanent magnet is not assisted with the electromagnet.
Furthermore, once the driving-side rotator and the driven-side rotator are coupled with each other, the coupled state of the driving-side rotator and the driven-side rotator is maintained by the attracting force of the permanent magnet. Therefore, the unnecessary conduction of the drive force, i.e., the erroneous operation of the clutch mechanism occurs.
For example, when the clutch mechanism of the self retaining type, which is recited in Japanese Examined Patent Publication No. H02-002007B, is applied to the refrigeration cycle system of the vehicle air conditioning system to enable or disable the conduction of the drive force to the compressor, the size of the gap may possibly be reduced by the vibration of the engine or of the vehicle body. When the driving-side rotator on the engine side and the driven-side rotator on the compressor side are coupled with each other due to the reduction in the size of the gap between the driving-side rotator and the driven-side rotator, the unnecessary conduction of the drive force from the engine to the compressor occurs.